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Pol 02 NOx emissions

Number of credits available Minimum standards

Building type dependent

No

Aim

To contribute to a reduction in national NOx emission levels through the use of low emission heat sources in the building.

Assessment criteria

The following is required to demonstrate compliance:

Up to three credits (all building types except Industrial)

  1. Where the plant installed to meet the building’s delivered heating and hot water demand has, under normal operating conditions, a NOx emission level (measured on a dry basis at 0% excessO2) as follows:

NOx Emission levels for heating and hot water (mg/kWh)

Credits

100 mg/kWh

1 credit

70 mg/kWh

2 credits

40 mg/kWh

3 credits

Two credits (Industrial building types only)

NOx Emission levels for heating and hot water (mg/kWh)

Credits
Office and associated areas 70 mg/kWh 1 credit
Operational areas 70 mg/kWh 1 credit
  1. Report via the BREEAM scoring and reporting tool the direct and indirect NOx emissions in mg/kWh and energy consumption in kWh/m²/yr arising from systems installed to meet the building's space heating, cooling and hot water demands.

Checklists and tables

None.

Compliance notes

Ref

Terms

Description

Shell and core

CN1 

Applicable assessment criteria

Option 1 – Shell only: This issue is not applicable.

Option 2 – Shell and core: All criteria relevant to the building type and function apply.

Refer to Appendix D – BREEAM UK New Construction and Shell and Core Project Assessments for a more detailed description of the above shell and core assessment options.

Simple buildings

CN2 

Applicable assessment criteria All criteria relevant to the building type and function apply.
General

CN3 

New build extensions to existing buildings If the heating/hot water demand for the new extension is being met by an existing system, then the NOx emission level for the existing system must be assessed against the criteria of this issue.

CN3.1 

Highly insulated building Where the heating load for a highly insulated building is less than or equal to 7% of the heat load for a Building Regulations compliant building of the same size and type, one credit can be awarded regardless of the NOx emission level. Figures used for calculations of the percentage of total heat demand must be based on the output from approved building energy calculation software.

CN3.2 

NOx data provided in different units Where NOx data is provided in different units or at a level of excess oxygen greater than zero, the manufacturer/supplier must be asked to convert this to comply with the BREEAM criteria. Alternatively, the assessor may adjust the figure using the relevant correction factors provided in the Pol 02 NOx emissions section. Note that the conversion factors provided do not apply where combined heat and power (CHP) systems are being assessed. Where CHP systems are used, the information must be obtained from the system manufacturer.

CN3.3 

Grid electricity Where grid electricity is used to supply a heating system, the NOx emissions should be assumed to be 617 mg/kWh for the purpose of BREEAM. This is to reflect the likely NOx emissions from grid electricity over the next 10 years based on the predicted generation mix in the UK.

CN3.4 

Heat recovery Heat recovery can be considered as having zero NOx emissions for the purpose of this issue.

CN3.5 

Open flues No credits may be awarded for open flue heating or hot water systems.

CN3.6 

Water heating benchmark and point of use heaters

Where the water heating can be demonstrated to be less than 10% of the building's total energy consumption, these credits can be awarded based solely on the NOx emissions from space heating.

CN3.7 

Assessment and reporting of a building's NOx emissions from cooling

At present the Pol 02 issue does not benchmark and award credits for NOx emission levels associated with a building's cooling demands. To facilitate possible future benchmarking of this kind and alignment with European Standards on the Sustainability of Construction Works, BREEAM does require, as a condition of achieving any credits for this issue, the reporting of both direct and indirect NOx emissions resulting from meeting the building's heating, cooling and hot water demands.

In the case of indirect emissions, this refers primarily to emissions associated with grid electricity, where grid electricity is a/the source of energy for the building's heating, cooling and/or hot water demands. Direct NOx emissions are those resulting from the burning of fuel on-site or in the assessed building to meet heating, cooling and/or hot water demands, for example via a gas/oil-fired/biomass boiler.

Building type specific

CN4 

Industrial

Office/operational areas not present

First credit: Where the assessed building is designed without an office area, the first credit does not apply. One credit is therefore available where compliance with the operational area benchmark is met.

Second credit: Where the operational area of the assessed building is designed to be untreated, the second credit does not apply. One credit is therefore available where compliance with the office area benchmark is met.

Where there is no office area and no heating in the operational area, this issue is not assessed.

Methodology

Conversion factors

Manufacturers should be asked to supply NOx emissions data in mg/kWh, measured on a dry basis. Where this is not possible the assessor may use the following conversion factors to convert figures in parts per million (ppm), mg/MJ, mg/m³ or wet NOx.
It should be noted that these conversion factors assume worst case efficiencies and are likely to give conservative answers. This could have the effect of lowering the number of credits achieved. Note that these conversion factors are not applicable where combined heat and power (CHP) systems are being used. Please see the calculation procedures below for further details on assessing CHP systems for this issue.

  1. Figures in mg/m³ should be multiplied by 0.859 in order to convert emissions into mg/kWh1BS EN 15502-1:2012 Gas-fired heating boilers Part 1: General requirements and tests.. A conversion may also be necessary for data not calculated at 0% excess oxygen (see below).
  2. Figures in ppm should be multiplied by 1.76 in order to convert emissions into mg/kWh. A conversion may also be necessary for data not calculated at 0% excess oxygen (see below).
  3. Figures in mg/MJ should be multiplied by 3.6 in order to convert emissions into mg/kWh (1 kWh = 3.6 MJ). A conversion may also be necessary for data not calculated at 0% excess oxygen (see below).

Wet NOx conversion factor

This issue’s criteria are based on dry NOx values – almost all manufacturers will quote emissions measured on a dry basis. However, if wet NOx figures are supplied, these will need to be converted to dry. The following formula should be used to determine the wet NOx conversion factor2BS EN 14792:2005 Stationary Source emissions - Determination of mass concentration of nitrogen oxides (NOx) - Reference method: Chemiluminescence.:

Conversion factor c = 100/(100-y)

Where y is the % water vapour content measured in the gas. This figure should be obtained from the manufacturer.

Excess oxygen correction

If a NOx emission rate is quoted by the manufacturer in mg/m³ or ppm, then it should be established at what percentage excess oxygen this emission was measured. The greater the amount of excess oxygen in the flue gases at the time of measurement, the more 'diluted' the NOx emissions. It is therefore important to convert any emission rate back to 0% excess oxygen. For the purpose of BREEAM, the following conversion factors can be used for the most frequently used rates supplied by manufacturers:

Table 62 Excess oxygen conversion factors

% Excess O2 Conversion (c)
3% x 1.17
6% x 1.40
15% x 3.54

Conversion factor c = 20.9/(20.9 – x)

Where x = % excess O2 (NOT excess air) and 20.9 is the percentage of O2 in the air.

Calculating NOx emission levels from combined heat and power (CHP) systems

Where CHP systems are specified, it is only necessary to consider the heat-related NOx emissions for the assessment of this issue.

NOx emissions are allocated to heat and electricity in line with the electrical output and the relationship between the heat input and the heat output. A NOx emission rate equivalent to the current rate for grid electricity should be assumed for the electrical output (i.e. 617 mg/kWh supplied), and the remaining NOx should be allocated to the heat input. Only the heat-related component is then compared with the benchmark scale. The following formula should be used to determine this:

X = (A - B)/(C/D)

Where:

Term Description
X NOx emissions per unit of heat supplied (mg/kWh heat).
A NOx emissions per unit of electricity generated (mg/kWhelec), i.e. the NOx emitted by the CHP system per unit of electricity generated. It is essential that this figure is obtained from the installer/supplier of the system and should be based on the system when operating at full load.
B NOx emissions per unit of electricity supplied from the grid (mg/kWhelec) this should be assumed to be 617 mg/kWh.
C Heat to Electricity Ratio of the CHP scheme.
D Overall system efficiency (%). When carrying out the calculation, enter the figure as a decimal, e.g. if the efficiency is 80%, then enter 0.8 into the calculation.

The above methodology determines the net NOx emissions from CHP-generated electricity compared with central generation of electricity and allocates this amount to the heat production. Where x is calculated to be negative, it should be assumed to be zero.

Calculating the average NOx emission levels from multiple systems

Where the CHP or other heating system type operates in conjunction with another system, an average NOx emission rate should be used based on the ratio of power output from each source, i.e. multiply the emissions of each system by the percentage of heat demand it supplies and total these values.

This is likely to be the case where a CHP system has been sized on the base power demand rather than the heat demand and therefore a secondary heating system is required.

The following formula can be used for such cases:

Contributing NOx emmisions from a heat pump formula

Where:

Term Description

N1

NOx emissions rate for source 1
N2

NOx emissions rate for source 2

Nn NOx emissions rate for source n
HT

Total heat output from all sources

H1

Heat output from source 1

H2

Heat output from source 2

Hn

Heat output from source n

Calculating NOx emission levels from heat pumps

For the purpose of assessing this BREEAM issue, either of the formulas below can be used to determine the contributing NOx emissions from a heat pump:

Formula to determine the contributing NOx emissions from a heat pump

Where:

Term Description
MHeat NOx emissions per unit of heat generated in mg/kWhHeat
MElec NOx emissions from UK grid electricity mg/kWh, this should be assumed to be 617 mg/kWhElec
WElect Total quantity of electricity consumed by heat pump kWhElec

WHeat

Total quantity of heat produced by heat pump kWhHeat
EER Energy Efficiency Ratio (also referred to as Co-efficient of Performance)

Evidence

Criteria Interim design stage
Final post construction stage
All

One or more of the appropriate evidence types listed in The BREEAM evidential requirements section can be used to demonstrate compliance with these criteria.

1, 2 Calculations showing the average NOx emissions for the building where multiple systems are present. As per interim design stage

Additional information

Relevant definitions

Approved building energy calculation software
Refer to BREEAM issue Ene 01 Reduction of energy use and carbon emissions
NOx emissions
NOx emissions are pollutant gases produced by the combustion of fossil fuels. NOx reacts with heat and sunlight to produce ozone that can cause serious respiratory problems. It also reacts with water to produce acid rain which has a detrimental effect on ecosystems. For the purposes of BREEAM, NOx emission levels are required in units of mg/kWh, measured on a dry basis at 0% excess oxygen levels.

Other information

Some systems may find it difficult to achieve credits in this issue, including:

Heat pumps

Heat pumps powered by grid electricity are likely to indirectly produce emission rates higher than those required by BREEAM and are therefore typically unable to achieve credits under this issue. However, there is a formula for determining NOx emissions from heat pumps in the Pol 02 NOx emissions section. Please note, the energy saved by using certain types of heat pumps is recognised in the energy section of BREEAM.

District heating

District heating systems that incinerate waste usually have NOx emission rates higher than the levels set to achieve any BREEAM credits.

Biomass

Biomass systems are recognised as reducing the impact of fossil fuel depletion by employing a renewable fuel source (provided it is sustainably sourced). However, biomass can produce a significant amount of NOx and so may not achieve this credit. They may, however, gain recognition in the energy section of BREEAM.


BREEAM UK New Construction non-domestic buildings technical manual 2014
Reference: SD5076 – Issue: 5.0
Date: 23/08/2016
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